Transcriptional control of the DNA methyltransferases is altered in aging and neoplastically-transformed human fibroblasts
Transcriptional control of the DNA methyltransferases is altered in aging and neoplastically-transformed human fibroblasts
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DOI：
10.1023/a:1025548623524
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发表时间：
2003-10-01
影响因子：
4.3
通讯作者：
Tollefsbol, TO
中科院分区：
文献类型：
--
作者：
Casillas, MA;Lopatina, N;Tollefsbol, TO
虽然很长一段时间以来我们都知道基因组甲基化在衰老和肿瘤组织和细胞中会发生显著改变，但导致这些改变的潜在机制尚不清楚。由于DNA甲基化影响许多不同的细胞过程，包括最重要的基因表达，因此阐明衰老和癌症中DNA甲基化异常的基础是重中之重。为了解决这个问题，我们试图分析衰老和肿瘤转化的WI-38人胎儿肺成纤维细胞中三种主要DNA甲基转移酶（Dnmt1、3a和3b）的基因表达、蛋白质产生和酶活性的变化。我们发现，这三种Dnmts的基因表达不仅在衰老细胞中，而且在使用特定遗传元件诱导进行肿瘤转化的WI-38成纤维细胞中，Dnmts的蛋白质产生和酶活性的变化都是相似的。这些发现强烈暗示基因表达的变化是这些细胞基因组甲基化改变的潜在机制。衰老细胞中dnmtts基因表达发生显著变化，Dnmt1 mRNA减少，而Dnmt3b mRNA稳步增加，这与我们在这些酶的蛋白质产生和活性方面的观察结果一致。令人惊讶的是，在衰老细胞中，Dnmt3a的基因表达实际上减少了。因此，我们提出Dnmt1的转录控制，主要的维持甲基转移酶，在衰老细胞中被显著抑制，并有助于减少这些细胞的基因组甲基化。衰老细胞中偶发性基因的高甲基化似乎与Dnmt3b基因的转录上调有关。此外，我们试图探索这些Dnmts在早期细胞转化中基因表达、蛋白质产生和酶活性的协调变化。在这些细胞中，所有三种主要Dnmt的基因表达均上调，随后Dnmt蛋白和酶活性显著增加。因此，这些结果共同表明，dnmt转录控制的变化可能是衰老细胞和肿瘤发生细胞中DNA甲基化已知变化的原因。他们还表明，Dnmt1和Dnmt3b的转录变化可能是影响衰老细胞中普遍低甲基化和特异性高甲基化的最重要因素，而所有Dnmts的基因表达在癌细胞中显著增加。这些发现应该对阐明衰老和肿瘤发生中DNA甲基化变化的潜在原因具有广泛的意义，并指出个体dnmt基因表达的变化可能是这些过程中涉及的一种机制。
Although it has been known for quite some time that genomic methylation is significantly altered in aging and neoplastic tissues and cells, the underlying mechanisms responsible for these alterations are not yet known. Since DNA methylation affects many different cellular processes including, most significantly, gene expression, elucidation of the basis for aberrations in DNA methylation in aging and cancer is of high priority. To address this problem, we sought to analyze changes in gene expression, protein production and enzyme activity of the three major DNA methyltransferases (Dnmt1, 3a, and 3b) in aging and neoplastically-transformed WI-38 human fetal lung fibroblasts. We have found that the gene expression of each of the three Dnmts parallels changes in protein production and enzyme activity of the Dnmts not only in aging cells, but also in WI-38 fibroblasts induced to undergo neoplastic transformation using defined genetic elements. These findings strongly implicate change in gene expression as an underlying mechanism in the altered genomic methylation of these cells. Striking changes in the gene expression of the Dnmts were observed in aging cells with the mRNA of Dnmt1 becoming reduced while the mRNA of Dnmt3b increased steadily in aging cells consistent with our observations in protein production and activity of these enzymes. Surprisingly, Dnmt3a actually decreased in gene expression in aging cells. We therefore propose that the transcriptional control of Dnmt1, the predominant maintenance methyltransferase, is significantly suppressed in aging cells and contributes to the reduced genomic methylation of these cells. The paradoxical sporadic gene hypermethylation in aging cells appears to be related to transcriptional up-regulation of the Dnmt3b gene. In addition, we sought to explore the coordinated changes in gene expression, protein production, and enzyme activity of these Dnmts in early cellular transformation. In these cells, the gene expression of all the three major Dnmts were up-regulated followed by marked increases in Dnmt protein and enzyme activity. These results therefore collectively indicate that changes in transcriptional control of the Dnmts are the likely cause for the known alterations in DNA methylation in aging cells and in cells undergoing tumorigenesis. They also show that changes in transcription of Dnmt1 and Dnmt3b are probably most important in affecting the generalized hypomethylation and specific hypermethylation seen in aging cells while gene expression of all the Dnmts is significantly increased in cancer cells. These findings should have broad implications in elucidating the underlying causes of changes in DNA methylation in aging and tumorigenesis and point to variations in gene expression of the individual Dnmts as a likely mechanism involved in these processes.